Testing circuit



March 11, 1941.

E. B. MORROW 2,234,272-

TESTING CIRCUIT Filed July '12, 1939 147 TOR/V5 Patented Mar. 11, 1941 UNITED STATES TESTING CIRCUIT Edward B. Morrow, Chicago,

Ill., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application July 12, 1939, Serial No. 283,953

9 Claims.

This invention relates to testing circuits and more particularly to circuits for testing telephone switching units.

It is an object of the present invention to provide a simple and eflicient testing circuit for testing telephone exchange equipment.

In accordance with one embodiment of the invention as applied to private exchange link and trunk units, which, in their operation in connection with the completing of telephone calls, automatically place potential on some leads of the circuit in the units and operate relays therein in predetermined sequences, a circuit is provided for checking simultaneously for the presence of potential on certain leads in the telephone eX- change unit and the absence of potential on all other leads in the unit. The circuit includes a series of differential relays arranged so that a stepper switch which controls the operations of the relays of the unit under test will automatically make one test after another of the unit as long as the unit under test operates correctly, but which will interrupt the automatic testing operation when any of the circuits in the unit under test have potential on leads therein which should not be present at that stage of the test or when they have no potential on them at a time during the test when they should have potential on them.

A better understanding of the invention will be had by reference to the accompanying drawing, wherein the single figure shows schematically a testing apparatus for checking for the presence or absence and polarity of potential on leads in an automatic telephone switching unit.

Referring to the drawing, wherein like reference characters designate similar parts throughout the several views, a selector switch, designated generally by the numeral 5, comprises a plurality of arcuate banks of contacts 6, I and 8 having brushes 9, I and H associated therewith, respectively. The brushes 9, I0 and II are mounted upon a common shaft, indicated by dot and dash lines at I2, and are actuated by a stepper magnet I3.

A start switch I4 is provided for initiating testing operations in the testing circuit shown at the left hand side of the drawing and designated generally by the numeral I5. Upon operation of the start switch I4, the testing apparatus I5 will test the operation of a telephone switching unit, a portion of which is shown, designated generally IS. The telephone switching unit has been shown diagrammatically and as so shown comprises a series of relays I'I, I8, I9 and 20,

which, when connected to other telephone equip 'ment, will operate to automatically complete a understood that the leads 2|, 22, 23 and 24, ex-

tending from. the switching unit I6, are those leads which would either be connected to the subscribers telephone equipment or other parts of telephone exchange equipment. Prior to the start of the testing operations, these leads may be connected by any suitable means, not shown, but illustrated by the dotted lines, to leads 25, 25, 2'! and 28 in the testing apparatus l5.

The right hand bank of contacts 8 of the stepper switch 5 have a series of leads extending therefrom, designated by the numerals 29, 30, 3| and 32. These leads may be connected to leads 33, 34, 35 and 36 in the switching unit to be tested, and upon step by step operation of the brush II under control of the stepper magnet I3, the brush II will connect ground at 31 to one side of the winding of the relays II, I8, I9 and 29 in automatic succession. The other side of the windings of the relays I'I, I8, I9 and are connected to grounded battery and the relays should therefore operate in succession.

Since it is a function of the relay IT, in its intended operation in the switching unit I5, to,

upon operation, place ground on lead 2| and 30 grounded battery on lead 22 over the break contact of relay I8, the arrangement of the testing apparatus is such that it will, in the first oper'ative position of the selectorswitch, test lead 2| for ground potential and lead 22 for a grounded battery connection. Since relays I8, I9 and '20 are at this stage of the operation not supposed to be energized, it will check lead 23 and lead 24 for the absence of either grounded battery or ground, respectively, on those leads. manner, operation of relay l8, which occurs at the second operative position of selector switch 5, should break the circuit to lead 22 through its break contact and place grounded battery on lead 23, and the relays I9 and 2B are not supposed to be operated. Therefore, lead 22 should have no potential on it, the lead 23 should' be connected to grounded battery, the lead 24 should have'no potential on it and lead 2| should have ground on it since relay II should remain locked up over break contact of relay I9 and its own locking contact. In position 3 of the selector switch, the desired condition is to have grounded battery on' lead 22, no potential on lead 2|, ground on lead 24, and no potential on lead 23, and whilerela'y In like foo be more clearly understood if the general de-' scription of the apparatus and the description of the operation thereof are combined. After the switching unit I6 to be tested has been connected.

to the testing apparatus I5, as indicated-by the dotted lines, the start key M may-"be-closed to place ground on the secondary winding S-of four differential relays 40, 4|, 42 and 43. The other side of the secondary windings of each of these relays is connected to grounded .battery, as indicated at 48, 49, 50 and 5|, respectively, resistances 44 and 4'! being connected between. the grounded batteries 48 "and 5| and their respective secondary windings'and resistances 45 and.46 being connected between. the secondary windings S of relays 4| and 142'and ground at the key |4. The closure of key, M therefore will initiate the testing operationbyoperating relays 43,. 4|, 42 and .43,'the operation of these relays then connecting ground at v52 through the make contacts of the relays 4|], 4|, 42 and 43 and an interrupter contact 53 associated -with the stepping electromagnet l3, through the winding of the electromagnet |3 to grounded batteryat 54. The electromagnet |3 will cause the brushes 9, l and H to step out of their normal position, as shown, into position When the selector switch. brushes 9, l0 and II step-toltheir. first position, the brush 9 will cornnofjtrpletev a circuit from grounded battery at 60,

thereby; short circuiting the secondarywinding of the relay 42; brush H), in its first position, will place ground on one side of. the secondary windingeoflthe relay 43-50 .that in position I of the selector. switch,- the secondary windings of therelays 43 and 42 will be-deenergized; However, if the relay I! in the unit under test has operated asit should, ground at relay i! will be connected over leads2| and 25-through the pri- Y Emary winding P of' relay and a resistance 6| to grounded battery at and grounded battery associated with thebreak contact of relay 3 willbe connected over a'make contact of relay I'L leads 22 and 26, through the primary. winding-P of relay 4 2 and resistance 52 to ground at key M;-

Inpositionl 'of the-test, relays l8, Hand 29 should. not be operated and therefore the grounded battery at relay I8 should not be connected-to the primary winding of relay 4| to opposethesecondary winding of this-relay and'in likemanner groundat the makecontacts of relays --|9 and 20 should not beconnected to'the primary winding of relay 4|] to energize that windingrso'that it would oppose the secondary winding; Therefore, if the unit under test operatestsatisfactorily in position I, the test will proceed due .to the completion of a circuit from ground'*at'.'52through the make contacts of re-.

lays'-t:4||;.-'4|,- 42 and 43, interrupter contact 53, winding. ofrelectromagnet I3 to grounded battery atii54; thereby to step the brushes 9, l0 and into position 2. It should be noted that relay'll when energized will lockup to ground at relay-|9..'u'nti1. relay I9. is operated.

will not fall back since it will remain energized over its primary winding P from ground at relay due to the fact that relay IT is locked up overthe circuit from grounded battery at relay H, the right hand make contact of relay H to ground at the break contact of relay l9. Therefore, in position 2, relay 43 will be held energized unless relay |9 operates, relay 42 will be held on ergized over its secondary winding, relay 4| will be held energized over its primary winding from grounded batteryat make contact of relay I8, leads 23 and 2'| through primary winding of relay 4| anda resistance 63 to ground at the start key 4. Relay 4i] will be held energized in position 2 because relay l9 and relay 2!] did not operate to place either of the grounds at their make contactsonone sideof the primary winding of relay 4!). If, in position 2, of the test, relay remains energized over its locking path and relayl8 isthe onlyrelay energized by brush connecting groundlto its Winding, the double wound renystarn 42and 43 will all be energized and the circuit to the electromagnet |3 will again be completed to step thebrushes 9, H1 and i and selector switch 5 into position 3. 1 When thebrushes 9, l0 and I arrive in position3, brush 9 will place grounded battery on the. secondary winding of. relay 42 .to-again short circuit that winding, brush will placeground on the secondary winding of. relay 4!] to-short circuit. that Winding, and brush Will.place ground-overload 34 to the windingofrelay l9 to energize-it. The. energization of relay I9 breaks the locking ground which held relay energized, thereby removing ground fromthe pri-- mary winding .of relay 43, places ground on one side of the primary winding'of relay 40, the other side of the winding of which is connected through the resistance 64 to. grounded battery at 48.

ance 62 to ground at the start key l4. Relays 43 and 4| should at this time, be energized over their secondary windings if relays |8-and are notenergized since-no short circuit will be initiated and the windings of these relays will not 'buck'one another.

Since all. of the relays 40, 4|, 42 and 43 willbepulled up if the unit under testis operating'correctly,'electromagnet I3 will again be energized to step its brushes to position4; in which position brush 9 is ineffective. Brush ID will connect ground to one side of the secondary'winding'of relay 40to short circuitthe secondary winding of relay 40 and brush II will connect ground to operate relay 2| Relay 2| operated will place groundlon the primary Winding of relay 40 to energize it. If relays l8 and 19 are not operated at this time, the secondary windings of re1ays'4l, 42 and 43 will operate these relays and the brushes 9, I0 and U will therefore stepto their 5th position.

The'contacts of the bank 1 associated withthe brush Ill in positions 5 to 2!], inclusive, arethe'first of these contacts, ground will be connected to the interrupter contact 53 associated with the 'electromagnet l3 to cause the electromagnet to buzz or step its associated brushes 9,

l0 and II forward to position 2| without affect-.

ing the rest of the circuit. In position 2!, the brush II will connect ground through a lamp 10 to grounded battery at H to light the lamp, thereby indicating that the switching unit under test in its various operations placed ground or battery on the proper leads 2|, 22, 23 and 24 or had no potential on those leads when no potential should have been on them. The operator may then release the start key M and in so doing, the left hand pair of contacts of the start key M will connect ground through brush ID, the left hand contacts of key I4, which are normally closed, through the interrupter contact 53 of the electromagnet l3 to cause the brushes 9, l0 and H to step back to normal position, as shown, thereby to place the test set in condition for another testing operation.

Although a specific embodiment of the invention has been described hereinbefore, it will be understood that various modifications thereof may be made without departing from the scope of the appended claims.

What is claimed is:

1. An apparatus for testing telephone switching units comprising a series of differential relays, a switch for normally energizing the secondary windings of said relays, a selector switch operable under control of said relays for supplying potential to various parts of the unit under test and for selectively supplying potential to short circuit the secondary windings of said differential relays, and a plurality of leads extending to the unit under test for energizing the primary windings of said relays in a predetermined order.

2. An apparatus for testing telephone switching units comprising a series of differential relays, a switch for normally energizing the secondary windings of said relays, a selector switch operable under control of said relays for supplying potential to various parts of the unit under test and for selectively supplying potential to short circuit the secondary windings of said differential relays, and a plurality of leads extending to the unit under test for energizing the primary windings of said relays in a predetermined order, said selector switch and leads from the unit under test cooperating to energize only one winding of each differential relay when the unit under test operates correctly to continue operation of the testing apparatus.

3. An apparatus for testing telephone switching units comprising a series of differential relays, a switch for normally energizing the secondary windings of said relays, a selector switch operable under control of said relays for supplying potential to various parts of the unit under test and for selectively supplying potential to short circuit the secondary windings of said differential relays, and a plurality of leads extending to the unit under test for energizing the primary windings of said relays in a predetermined order, said selector switch and the leads extending to the unit under test serving to maintain ing potential to various parts of the unit under test and for selectively supplying potential to short circuit the secondary windings of said differential relays, and a plurality of leads extending to the unit under test for energizing the primary windings of said relays in a predetermined order, said selector switch and the leads extending to the unit under test serving to maintain only one winding of each differential relay energized if the unit under test operates correctly to maintain the energizing circuit of the selector switch.

5. An apparatus for testing telephone switching units comprising a series of differential relays, a switch for normally energizing the secondary windings of said relays, a selector switch operable under control of said relays for supply in potential to various parts of the unit under test and for selectively supplying potential to short circuit the secondary windings of said differential relays, and a plurality of leads extend-' ing to the unit under test for energizing the primary windings of said relays in a predetermined order, only one Winding of each differential relay being connected to be energized either by the selector switch or by the unit under test if the unit under test operates correctly.

6. An apparatus for testing telephone switching units comprising a series of differential relays, a switch for normally energizing the secondary windings of said relays, a selector switch operable under control of said relays for supplying potential to various parts of the unit under test and for selectively supplying potential to short circuit the secondary windings of said differential relays, and a plurality of leads extending to the unit under test for energizing the pri-' mary windings of said relays in a predetermined order, said selector switch being adapted to supply potential of a predetermined polarity to the secondary windings of said differential relays in a predetermined order and said leads from the unit under test being adapted to supply potential of a predetermined polarity to the primary windings of the differential relays in a predetermined order.

'7. An apparatus for testing telephone switching units comprising a series of differential relays, a switch for normally energizing the secondary windings of said relays, a selector switch operable under control of said relays for supplyin potential to various parts of the unit under test and for selectively supplying potential to short circuit the secondary windings of said differential relays, a plurality of leads extending to the unit under test for energizing the primary windings of said relays in a predetermined order, said selector switch being adapted to supply potential of a predetermined polarity to the secondary windings of said diiferential relays in a predetermined order and said leads from the unit under test being adapted to supply potential of a predetermined polarity to the primary windings of the differential relays in a predetermined order, and a brush on said selector switch for controlling the sequence of operation of the various parts of the unit under test for controlling the order in which potential is supplied to the primary windings of the differential relays.

8. An apparatus for testing telephone switching units for the presence or absence and polarity of potential on the leads thereto during the operation thereof comprising means for supplying operating potential to the actuating relays in a unit in automatic succession, a plurality of dif-' ferential relays havinggtheir primary ,Windings connected to theleads to :be. tested, andca sele'ctonswitchrfor controlling the supply of potentiaLtothe unit under test and'to the secondary windings of'the-difierential relays.

' 9; An; apparatus :for testing telephone switching-units for the presence or absence and polarity of: potential onthe leads thereto during the -operation: thereof comprising: means for supplying 5 operating potential togthe actuating relays in a unit. in automatic succession, a pluralityhof vdif.-

ferential relays having'theinprimary windings.

EDWARD, B. MORROW; 

